Whip antenna with adjustable tuning



Oct. 21, 1969 F. E. IRELAND WHIP ANTENNA WITH ADJUSTABLE TUNING 2Sheets-Sheet 1 Filed July 10, 1968 FIGZ INVENTOR FRANK IRELAN D FlG.l

ATTORNEY Oct. 21, 1969 F. E. IRELAND WHIP ANTENNA WITH ADJUSTABLE TUNING2 Sheets-Sheet 2 Filed July 10. 1968 m M m I w 1 M F l 6 Ell v F 3 4 5 44 j T /III L '6 rr E F mvsmon FRANK IRELAND United States Patent Int.Cl. Hlllq 9/06 US. Cl. 343-745 16 Claims ABSTRACT OF THE DISCLOSURE Thisdisclosure describes a high frequency antenna that includes a noveltuning means mounted in the antenna for tuning the antenna to aparticular frequency band. The antenna includes at least one antennaelement electrically connected to the tuning means. Electrically, thetuning means comprises a variable capacitor connected in parallel withan inductor. Mechanically, the tuning means comprises a tubular metallicshield mounted about an inductor coil. The shield is longitudinallymovable, and, when moved, varies the capacitance between the shield andthe coil and elements connected to the coil. Alternatively, a tuningslug is mounted in the coil and moves with respect to the coil so as tovary the inductance of the coil.

This application is a continuation-in-part of US. patent applicationSer. No. 515,611, filed Dec. 22, 1965, now abandoned.

This invention relates to high frequency antennas and more particularlyto a vertical mobile antenna havlng an improved radiating and/orreceiving characteristic.

The prior art teaches that the well-known ground plane antenna composedof a vertical quarter-Wave radiating and/ or receiving element workingagainst a quarter-wave characteristic horizontal ground plane has a highangle of radiation lobe pattern. It is also well known that a high angleof radiation is desirable for in flight communicauon with aircraft, butthat there is a corresponding sacrifice in signal strength at groundlevel when such an antenna is used for ground level or mobilecommunications.

Even though vertical quarter-wave radiating element antennas have theforegoing ground level disadvantage, it is customary to mount such anantenna on a mobile vehicle for mobile communications. Such an antennausually consists of a tubular electrically conducting structure whichmay rise to a height of 10 feet, for example. External means are usuallyprovided for matching a load impedance to the antenna impedance forimproving the radiating and/or receiving characteristic of the overallcommunications system at any one frequency.

It is also well known that it is often necessary to pro vide a singleantenna of fixed length which is capable of satisfactory operation overa broad band of frequencies. To cover a desired band of frequencies, theusual practice is to provdie an external means for adjusting theimpedance of a loading coil so that the antenna is nearly resonant at aparticular frequency. It will be appreciated by those skilled in the artand others that this operation is not only time-consuming but alsocumbersome since the radiating frequency may vary over a Wide band oreven different bands. Because of this variation, frequent adjustmentsare necessary.

In addition to teaching that a quarter-wave antenna element Workingagainst a horizontal ground plane having a quarter-wave characteristicradiates a vertical pattern, the prior art also teaches that a verticalantenna including a vertical half-wave element exhibits virtually rightangle radiation provided that the base of the antenna is elevated abovethe reflective effect of the earth or other surice rounding objects. Itis impossible, of course, to meet these height requirements in mobilecommuniaction antennas. Consequently, the best of the prior art antennasare greatly effected by the presence of earth or surrounding structures.

It Will also be appreciated that mobile antennas are subject to breakageand/or distortion as the result of striking the antenna against aforeign object. Hence, an electrically sectioned antenna composed of aplurality of parts is more economical and feasible than a solid antennahaving the same radiating characteristics.

It is therefore an object of this invention to provide a verticalantenna having virtually right angle radiation or receptioncharacteristics.

It is a further object of this invention to provide a vertical antennahaving substantially right angle radiation or reception characteristicsthat is independent of earth ground when attached to a motor vehicle.

It is a still further object of this invention to provide a verticalantenna having substantially right angle radiation characteristics thatis fed at one end to produce the highest maximum electro-magnetic field.

It is yet another object of this invention to provide a novel tuningdevice that cancels undesirable reactances.

It is yet another object of this invention to provide a tuning devicesuitable for use with an antenna that is mechanically rugged andelectrically uncomplicated.

It is still another object of this invention to provide a tuningapparatus suitable for use with an antenna that is adapted to tune theantenna to radiate and/or receive signals in a predetermined frequencyband.

In accordance with a principle of this invention, an antenna element isconnected to a tunable means. The tunable means consists electrically ofa capacitor connected in parallel with an inductor. The capacitorcomprises a sleeve element mounted over an inductor coil. The sleeveelement is axially movable so as to vary the area between the sleeve andthe coil and elements connected to the coil. The variation in areacreates a variable capacitance which varies the frequency of resonanceof the parallel combination to thereby tune the antenna.

In accordance with another principle of this invention, the antennaelement comprises a one-half wave length radiating element. Thehalf-wave length element is separably attached to the tunable means atone end and the other end of the tunable means is connected to asuitable mounting means.

In accordance with a further principle of this invention, the antennaelement consists of a pair of quarterwave length elements. Onequarter-wave length element is separably attached to one end of theturnable means and the other quarter-wave length element is separablymounted between the tunable means and a mounting means.

In accordance with yet another principle of this invention, the tunablemeans includes a slug mounted inside of the coil. The slug is movablewith respect to the coil so as to vary the inductance of the coil.

It will be appreciated from the foregoing description that the invetnionprovides a rather uncomplicated means for tuning an antenna. The tunablemeans is mechanically strong and electrically uncomplicated, merelyconsisting of a fixed ferrule and a movable sleeve mounted over a coil.The sleeve provides mechanical strength, ease of adjustment and a shieldfor the coil. But, most important, the sleeve provides a means ofadjusting capacity to a critical value to effect exact reactancecancellation. That is, tuning the antenna cancels undesirable reactancesto prevent power loss caused by undesirable reactances. In addition, byproviding a movable core inside of the coil, additional adjustment isprovided. Further, by forming the invention of separable components, theantenna elements can be easily exchanged for longer or shorter elementsas desired. In addition, if one of the elements is broken, it can beeasily replaced.

It will also be appreciated that when the antenna is mounted on a motorvehicle body, the body does not form a part of the overall antennaradiation system as it does with prior art antenna systems. That is,most existing vehicle antennas, whether one-quarter wave, one-half waveor five-eights wave, are dependent on the vehicle body as part of theradiating system. This invention provides an easily tunable antennasystem for cancelling reactance with little or no antenna loss that isindependent of a vehicle body as part of the antenna radiating system.

The novel features of the invention, as well as the invention itselfboth as to its organization and method of operation, will be bestunderstood from the following description when read in connection withthe accompanying drawings wherein:

FIGURE 1 is an assembled antenna illustrating one embodiment of theinvention;

FIGURE 2 is an exploded cross-sectional view of one embodiment of thetuning means of the invention;

FIGURE 3 is an electrical schematic representation of the embodiment ofthe invention illustrated in FIGURES l and 2;

FIGURE 4 is a schematic representation of the voltage distribution of anassembled antenna of the type illustrated in FIGURE 1 when tuned for aspecific frequency;

FIGURE 5 is an assembled antenna illustrating an alternative embodimentof the invention;

FIGURE 6 is an exploded cross-section of an alternate embodiment of thetuning means of the invention;

FIGURE 7 is an electrical schematic of the embodiment of the inventionillustrated in FIGURES 5 and 6; and

FIGURE 8 is a schematic representation of the voltage distribution of anassembled antenna of the type illustrated in FIGURE 5 when tuned for aspecific frequency.

FIGURE 1 is a view of an assembled antenna wherein an upper quarter-waveantenna element 11 is coupled to a lower quarter-wave antenna element bya tuning element 25. The upper quarter-wave element 11 has a coronainsulator 13 mounted on the upper end thereof. The lower quarter-waveelement 15 is movably attached to a mounting plate 17 by a universalconnector 19. Mounting plate 17 is shown as attached to a vehicle side21. A coaxial cable 23 connects the lower end of the element 15 with atransmitter/receiver (not shown).

One embodiment of the tunable portion 25 of the antenna is shown indetail in FIGURE 2. An insulated copper were 27 is wound to form a coilabout a fiberglass insulating core 29. A brass sleeve 31, havingexternal threads 33, a counter bore 35, and an internal tap 37, isattached to the core 29 by a pin 30, for example.

Electrical contact 39 is made between the coil 27 and the sleeve 31 byany of the well known methods such as brazing, spot welding, or silversoldering, for example.

A second tapped brass sleeve 41 having internal threads 43 and a counterbore 45 is attached to core 29 by a second pin 44. Electrical contact 44is made between the sleeve 41 and the coil 27 by any of the well knownmethods hereinabove set forth.

The internal threads 43 of the lower sleeve 41 are adapted to accept thethreaded portion of the lower antenna element 15. Likewise, thecounter-bore portion 35 of the upper sleeve 31 is designed to accept ashoulder portion 51 of the upper antenna element 11. A lower tappedportion of the upper element 11 is threaded into the tapped area 37 ofthe upper sleeve 31.

An adjustable conductive sleeve 53 having internal threads 55 iscooperatively mounted on the outer threaded portion of the upper brasssleeve 31. A locking nut 57 is also threaded on the upper brass sleeve31 and cooperates to maintain the adjustable sleeve 53 in a desiredposition.

An O-ring element 56 is mounted between the lower portion of theadjustable conductive sleeve 53 and the outer periphery of the lowerbrass sleeve 41. This O-ring maintains a capacitive separation betweenthe adjustable conductive sleeve 53 and the lower brass sleeve 41. Inaddition, the O-ring adds to the lateral strength of the overallstructure. The O-ring may be held in the adjustable conductive sleeve 53by an internal peripheral slot, for example.

The adjustable sleeve 53 in combination with the brass sleeve 41 and thecoil 27 forms an adjustable capacitor which is electrically connected inparallel with the coil 27. This parallel circuit will resonate at afrequency determined by the adjustment of the sleeve. The electricalcircuit which is representative of the foregoing mechanicalinterconnection is illustrated in FIGURE 3. That is, FIGURE 3illustrates a variable capacitor connected in parallel with a fixedcoil.

FIGURE 4 is a schematic representation of the instantaneous vectorvoltage of the antenna when tuned for maximum efficiency. Morespecifically, in order to achieve high radiating and/ or receivingcharacteristics for the antenna, it is necessary that the antenna betuned to cancel the reactance between points 59 and 61 shown in FIGURES3 and 4. This cancellation is performed by adjusting the tuning elementto a resonant or near resonant state for the frequency of operation. Inaddition to compensating for the reactancc that occurs in an idealsituation, it will be obvious to one skilled in the art that slightdeviations in reactance caused by incorrect antenna length is alsocompensated for by resonating the tuned circuit.

It will be appreciated by those skilled in the art and others that theprimary purpose of the tuned element is to perform the function of aquarter-wave shorted stub line wherein a 180 phase displacement existsacross the points of connection so that there is a non-radiatingquarterwave coupling between the two quarter-wave radiating elements.This results in a narrow radiation pattern that, as best understood, iscaused by the distorted top and bottom lobes which combine to form ineffect a vertical beam antenna. That is, the instant antenna is designedto lower the angle of radiation by separating the upper approximatequarter-wave radiating antenna element from the lower approximatequarter-wave radiating with a fixed coil and a variable air condenserwhich are mounted so as to form a parallel resonant circuit very closeto the operating frequency. This resonant circuit (or closely resonantcircuit) forms a tuned stub allowing maximum voltage to appear at thecenter of the coil with voltages of opposite instantaneous polarityappearing at both ends of the coil (or stub). This action separates theupper half of the antenna from the lower half of the antenna so twowaves are radiated forming a single complex wave front having aflattened lobe and therefore greater effective voltage gain in thedesired direction.

It will be appreciated that if either of the antenna elements 11 or 15are damaged, they may be easily replaced with similar elements becauseof the separable nature of the mechanical construction of the invention.

It will also be appreciated that once the tuned circuit is tuned usingthe variable capacitance, the locking nut is tightened to prevent anychange in tuning due to vibration and the like.

FIGURES 5-8 illustrate an alternative embodiment of the inventionwherein the lower quarter-wave antenna element is eliminated and theupper quarter-Wave antenna element is replaced by a one-half Wave lengthelement. In addition, the core is eliminate from the coil and a tuningslug 73 is inserted in a hollow space inside of the coil 27 and the core29. The tuning slug 73 is attached to a shaft 75 that is threaded in theupper sleeve 53. By rotating the shaft 75 the slug 73 is verticallymoved inside of the coil 27. Movement of the slug 73 varies theinductive effect of the coil 27 in a manner well known in the art. Ifdesired, a lock nut can be included for locking the setting of the slugin place. FIGURE 7 illustrates, electrically, the parallel arrangementof the variable capacltor sleeve arrangement heretofore discussed withrespect to FIGURE 2 and the coil of variable inductance 27. By providingan adjustable inductance in parallel with an adjustable capacitance, therange of the overall tuned circuit is increased. That is, the tuningelement illustrated in FIGURES 5 and 7 can be tuned to frequencies overa greater range than the tuning element illustrated in FIGURES 1-3.

While the frequency range of the embodiment of the invention illustratedin FIGURES 5-8 is increased, the operation of the invention remainsidentical to the embodiment of the invention illustrated in FIGURES l-4hereinabove discussed. That is, the tuned circuit is adapted to tune theantenna so that undesirable reactance is cancelled. The one-half wavelength element forms a pattern that has a flattened lobe and thereforegreater voltage gain in the desired direction-The tuning elementoperates as a stub. And, the adjustable sleeve 53 provides a shield sothat the radiation of the tuning element has no etfect on the overalloperation of the antenna.

It will be appreciated by those skilled in the art and others thatapplicant has provided a relatively uncomplicated and inexpensivetunable mobile antenna. Although specific structure has been described,it will be appreciated that the scope of this invention includes variouschanges and modifications not specifically discussed. For example, thetunable element illustrated in FIGURE 6 can be used with the embodimentof the antenna illustrated in FIGURE 1, i.e., an embodiment includingtwo quarter-wave length elements. Alternatively, the embodiment of thetuning element illustrated in FIG- URE 2 can be utilized with theembodiment of the antenna illustrated in FIGURE 5. Moreover, othertuning elements can be used. In addition, it will be appreciated thatmore than one tuned circuit can be utilized in the invention. That is,by properly stacking a plurality of tuned elements increased gain isprovided. Further, wide variations in the size and shape of theinductive and capacitive elements fall within the scope of theinvention. Moreover, bank winding, powdered iron cores and multiplatecondensers can be used in the invention when low frequency ranges are tobe covered by a transmitter and/or receiver connected to the antenna.Hence, the invention can be practiced otherwise than as specificallydescribed herein.

It will also be appreciated that the invention provides a convenient andeasy method of tuning an antenna through resonance. The critical pointmay be approached from either side with ease and the tuning sleeve maybe locked in a selected position.

In addition to its use as an antenna tuning element, the tuning elementherein disclosed is useful in other environments. For example, it can beused as a filter to reject spurious signals. Alternatively, it can beattached to a tower, building, tank or other conducting structure andtuned to cancel unwanted reactance. And, it will serve as a tuningelement in a gamma match stub.

What is claimed is:

1. An antenna tuning device comprising:

a longitudinal insulating core having a longitudinal axis;

a coil wound around the longitudinal axis of said core;

a first electrical conducting sleeve element mounted over one end ofsaid core so that it is in electrical contact with one end of said coil;second electrical conducting sleeve element mounted over the end of saidcore so that it is in electrical contact with the other end of saidcoil; and movable sleeve element mounted for longitudinal movement alongthe outer periphery of said first electrical conducting sleeve, saidmovable sleeve element extending over said core and coil to said secondelectrical conducting sleeve.

2. An antenna tuning device as claimed in claim 1 wherein the outerperiphery of said first electrical conducting sleeve is threaded and theinner periphery of said movable sleeve element is tapped.

3. An antenna tuning device as claimed in claim 2 including a lock nutcoacting with said first electrically conductive sleeve element and saidmovable sleeve element to lock said movable sleeve element inpredetermined positions.

4. An antenna tuning device comprising:

a coil having a longitudinal axis;

a slug movably mounted along said longitudinal axis of said coil;

a first electrical conducting sleeve element mounted so that it is inelectrical contact with one end of said coil;

a second electrical conducting sleeve element mounted so that it is inelectrical contact with the other end of said coil; and movable sleeveelement mounted for longitudinal movement along the outer periphery ofsaid first electrical conducting sleeve, said movable sleeve elementextending over said coil to said second electrical conducting sleeve.

5. An antenna tuning device as claimed in claim 4 wherein the outerperiphery of said first electrical conducting sleeve is threaded and theinner periphery of said movable sleeve element is tapped.

6. An antenna tuning device as claimed in claim 5 including a lock nutcoacting with said first electrically conductive sleeve element and saidmovable sleeve element to lock said movable sleeve element inpredetermined positions.

7. An antenna comprising:

a longitudinal insulating core having a longitudinal axis;

a coil Wound around the longitudinal axis of said core;

a first electrical conducting sleeve element mounted over one end ofsaid core so that it is in electrical contact with one end of said coil;

a second electrical conducting sleeve element mounted over the other endof said core so that it is in electrical contact with the other end ofsaid coil; movable sleeve element mounted for longitudinal movementalong the outer periphery of said first electrical conducting sleeve,said movable sleeve element extending over said core and coil to saidsecond electrical conducting sleeve; and

an antenna element electrically connected to said first electricalconducting sleeve element.

8. An antenna as claimed in claim 7 wherein the outer periphery of saidfirst electrical conducting sleeve is threaded and the inner peripheryof said movable sleeve element is tapped.

9. An antenna as claimed in claim 8 including a lock nut coacting withsaid first electrically conductive sleeve element and said movablesleeve element to lock said movable sleeve element in predeterminedpositions.

10. An antenna as claimed in claim 9 wherein said antenna element isformed of two quarter-wave length elements, one quarter-wave lengthelement electrically connected to said first electrical conductingsleeve element and the other quarter-wave element electrically connectedto said second electrically conducting sleeve element.

11. An antenna as claimed in claim 9 wherein said antenna element is aone-half wave length element.

12. An antenna comprising:

a coil having a longitudinal axis;

a slug movably mounted along said longitudinal axis of said core;

a first electrical conducting sleeve element mounted so that it is inelectrical contact with one end of said coil;

a second electrical conducting sleeve element mounted so that it is inelectrical contact with the other end of said coil;

a movable sleeve element mounted for longitudinal movement along theouter periphery of said first electrical conducting sleeve, said movablesleeve element extending over said coil to said second electricalconducting sleeve; and

an antenna element electrically connected to said first electricallyconducting sleeve element.

13. An antenna as claimed in claim 12 wherein the outer periphery ofsaid first electrical conducting sleeve is threaded and the innerperiphery of said movable sleeve element is tapped.

14. An antenna as claimed in claim 13 including a lock nut coacting withsaid first electrically conductive sleeve element and said movablesleeve element to lock said movable sleeve element in predeterminedpositions.

15. An antenna as claimed in claim 14 wherein said antenna element isformed of two quarter-Wave length elements, one quarter-wave lengthelement electrically connected to said first electrical conductingsleeve ele- References Cited UNITED STATES PATENTS 2,941,204 6/1960Bailey 343-745 2,059,186 10/1936 Brown 343-752 3,064,257 11/1962 Guest343--747 3,226,725 12/1965 Ritchie et al. 343--750 3,264,647 8/1966Nuttle 343750 ELI LIEBERMAN, Primary Examiner US. Cl. X.R.

